A mouse is a common button-type input device. Generally, the downward force required to trigger the tactile switch of the mouse is constant and fails to be adjusted. FIG. 1 is a schematic side view illustrating a button-type input device according to the prior art. As shown in FIG. 1, the input device 10 is a mouse. The input device 10 comprises a base 101, an upper cover 102, a click button 103, a tactile switch 104 and a circuit board 105. The tactile switch 104 is mounted on and connected to the circuit board 105. In response to a downward force exerted on the click button 103, the post-like pressing part 106 attached to the underside of click button 103 moves downwardly to touch the salient 107 attached on a top surface of the tactile switch 104. As such, a corresponding clicking operation is executed. Since the downward force for triggering the tactile switch of the mouse fails to be adjusted, a process of quickly clicking the click button for a long time period usually incurs unacceptable fatigue of the user's hand. As the demand on comfort of using the button-type input device is gradually increased, the conventional button-type input device is not satisfactory.